1. Field of the Invention
The present invention relates to a variable valve device for an internal combustion engine, in which the variable valve device variably sets a maximum lift amount of an engine valve.
2. Description of Related Art
In recent years, a variable valve device for variably setting a maximum lift amount of an engine valve has been put to practical use in an internal combustion engine. For example, a variable valve device described in Japanese Patent Application Publication No. 2004-339951 (JP 2004-339951 A) includes: a control shaft that determines a maximum lift amount of an engine valve based on a position in an axial direction; a cam that changes the position of the shaft; and an actuator that rotates the cam.
Further, JP 2004-339951 A describes that a retainer region where a cam diameter does not change is provided in a cam surface of the cam as well as a change region where the cam diameter increases gradually toward one side in a rotation direction. The variable valve device described in JP 2004-339951 A has such a structure that an axial force is caused in the control shaft due to a reaction force of a valve spring of the engine valve, so that a roller, which is an operation member attached to a camshaft, is pressed against the cam surface.
In the variable valve device, when the maximum lift amount of the engine valve is changed, the cam is rotated so as to move the roller on the change region. Further, when the maximum lift amount of the engine valve is retained, a phase of the cam is controlled so that the roller is placed in the retainer region. In a state where the roller, which is an action member, is pressed against the retainer region of the cam, the axial force of the camshaft acts on a cam surface perpendicularly, so that a torque by the axial force of the control shaft is hard to act on the cam. Thus, the variable valve device described in JP 2004-339951 A restrains the cam from being rotated due to the axial force of the control shaft, thereby easily retaining the maximum lift amount.
In the meantime, an actuator in which a deceleration mechanism constituted by a plurality of gears in combination is attached to a motor can be employed as the actuator for driving the cam, so as to decelerate a rotation of the motor via the deceleration mechanism.
In a state where the roller, which is an action member, is pressed against the retainer region of the cam due to a reaction force of a valve spring of the engine valve, the axial force of the camshaft acts on the cam surface perpendicularly, as described above. Accordingly, a torque due to the axial force of the control shaft is hard to act on the cam. At this time, a gap is easily caused between the gears because of backlash between the gears constituting the deceleration mechanism, which may cause gear rattle noise along with vibrations of the cam due to fluctuations or the like of the axial force of the control shaft.